The present invention relates to a contouring method and machine for printed circuits, said machine comprising an operating head movable with respect to the board supporting the circuits for cutting the contour of the printed circuits, and a workpiece pressing device for pressing the circuit during the cutting.
Normally printed circuits are obtained by effecting various operations such as drilling, plating the metallic layer, photoetching etc. on a glass resin board supporting the circuit, said board being larger than the final printed circuit. If the size of the circuit is small, a plurality of mutually similar or dissimilar printed circuits can be obtained from a single board. After the above mentioned operations, the board must be cut along the planned contour by an operation called contouring, which must be very precise to avoid any discontinuity, step or irregularity in the contour.
To this end either one board, or a stack of boards, is at first secured to the machine table by means of reference members. Then the operating head is commanded by a numerical control to be moved so as to cut the contour of each circuit. In these machines the problem is always faced of cutting the last contour portion of the circuit, because when this portion becomes smaller than a limit dimension, it can no longer hold the circuit stationary, whereby an irregularity or step is formed in the contour.
To obviate this disadvantage, in some known machines, the individual circuits are normally provided with a pair of reference members, so that during the cutting of the last portion the printed circuit remains locked by said reference members. However, these machines cause the preparation of the package of boards to be very long and intricate, due to the multiplicity of dimensions of the circuits and the plurality of pairs of reference members necessary for the various circuits.
It has also been proposed to replace the pairs of reference members of the individual circuits with two contour portions of the circuit having a length of a few millimeters, which portions are left in a first cutting operation of the head. For this latter proposal there is provided a workpiece pressing device comprising a pad, which during the first cutting operation slides on the board. Then the head is positioned again on the two individual portions, which are thus used as reference members, while the pressure of the pad is increased so as to clamp the board, whereby the pad must also be displaced with respect to the tool during the cutting of the two portions. Therefore, the pad is mounted on the head so as to be displaced a few millimeters with respect to the tool and is returned elastically to rest when the pressure terminates.
These latter machines have the disadvantage of requiring three positioning operations for the head, which in any case generate some irregularities in the cutting of the contour. Furthermore, due to the small size of said portions, betweeen the cutting of the first portion and the clamping of the circuit for the cutting of the second portion, the circuit can undergo some displacement unacceptable for the resulting contour. Finally, since the pad returns suddenly to rest when the pressure terminates, the circuits can be damaged thereby.